The invention relates to a hydraulic tensioning device for a traction mechanism drive, in particular for a chain or belt drive of an internal combustion engine, comprising a tensioning piston, which is guided in a displaceable manner in a cylinder, a pressure chamber, which is defined by the tensioning piston and the cylinder and which is used to receive hydraulic fluid, and a pressure relief valve, which limits the pressure in the pressure chamber.
In DE 40 35 823 C1, a hydraulic tensioning device for traction mechanism drives, such as chain or belt drives in internal combustion engines, is described. A tensioning piston pressed against the chain is held in a displaceable manner longitudinally in a cylinder. The tensioning piston and the cylinder define a pressure chamber for receiving hydraulic fluid. Tensioning movements of the tensioning piston in the direction towards the chain increase the size of the pressure chamber, and a non-return valve opens due to the low pressure set therein and motor oil can flow into the pressure chamber. Through tension from the chain, the tensioning piston is pressed inward, that is, away from the chain, wherein the pressure chamber becomes smaller. While the tensioning piston moves inward, motor oil is forced out of the pressure chamber through an overflow gap. The damping behavior of the tensioning device can be influenced by the size of the overflow gap. If the pressure in the pressure chamber becomes too large, the pressure relief valve opens.
A similar chain tensioner is known from DE 100 38 606 A1. The pressure relief valve of this chain tensioner is essentially formed by a valve ball, which is pressed by a compression spring against a valve seat formed on a bushing in the interior of the tensioning piston. If the pressure in the interior of the pressure chamber exceeds a set limit, the valve ball is pushed against the force of the valve spring, so that the motor oil can leak from the chamber. When the chain tensioner is assembled, the piston is located in the vertical position and the valve spring is used in the interior of the piston. Because the valve spring is not pre-tensioned in this state, the valve ball must be balanced on the valve spring until additional components are mounted. Therefore, it is very difficult to mount such a chain tensioner with an assembly robot without generating defects.